Cigarette filter with beaded carbon

ABSTRACT

A smoking article such as a cigarette comprises a tobacco rod and a filter component having a cavity filled with spherical beaded carbon. As mainstream tobacco smoke is drawn through the filter component, targeted gas phase smoke constituents are removed as the smoke passes through the carbon. During the filter manufacturing process the spherical beaded carbon flows like a liquid and substantially completely fills the cavity. Point-to-point contact between the spherical beads together with substantially complete filling of the cavity produces minimal channeling of ambulatory gas phase as well as maximum contact between the gas phase and the carbon surface of the spherical beads during smoking.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.10/339,680, filed Jan. 9, 2003. This application claims the benefit ofU.S. Provisional Application 60/347,558 filed Jan. 9, 2002, and U.S.Provisional Application 60/403,490 filed Aug. 14, 2002, which are herebyincorporated herein in their entirety by reference.

FIELD OF THE INVENTION

The present invention relates to filter-tipped smoking articles such asfiltered cigarettes, and in particular, to cigarette filters containinga carbon material.

BACKGROUND OF THE INVENTION

Filter-tipped smoking articles, particularly cigarettes, generallycomprise a tobacco rod, a filter and a band of tipping paper attachingthe filter to tobacco rod. The tobacco rod generally comprises a columnof shredded tobacco (e.g., in form of cut filler) that is wrapped withina cigarette paper or wrapper. Typically, the filter includes a plug offibrous material (a “filter plug”), preferably made of a celluloseacetate tow. Ventilation of mainstream smoke is achieved by provision ofa row or rows of perforations through the tipping paper at a locationalong the filter plug. Ventilation provides dilution of drawn mainstreamsmoke with ambient air to reduce the delivery level of tar per puff.

During smoking, a smoker draws mainstream smoke from the coal at the litend of the cigarette. The drawn cigarette smoke first enters theupstream filter portion of the filter and then passes through thedownstream portion adjacent to the buccal end of the cigarette filter.

Certain cigarettes have filter segments which incorporate materials suchas granules of carbon, silica gel, zeolite and the like. Exemplarycigarettes and filters are described in U.S. Pat. No. 2,881,770 toTovey; U.S. Pat. No. 3,353,543 to Sproull et al.; U.S. Pat. No.3,101,723 to Seligman et al.; and U.S. Pat. No. 4,481,958 to Ranier etal. and European Patent Application Nos. 532,329 and 608,047. Certaincommercially available filters have particles or granules of carbon(e.g., an activated carbon material) alone or dispersed within acellulose acetate tow; other commercially available filters have carbonthreads dispersed therein; while still other commercially availablefilters have so-called

cavity filter

or

triple filter

designs. Exemplary, commercially available filters include SCS IV DualSolid Charcoal Filter and Triple Solid Charcoal Filter from FiltronaInternational, Ltd.; Triple Cavity Filter from Baumgartner; and ACT fromFiltrona International, Ltd. See also, Clarke et al., World Tobacco, p.55 (November 1992). Detailed discussion of the properties andcomposition of cigarettes and filters is found in U.S. Pat. No.5,404,890 to Gentry et al. and U.S. Pat. No. 5,568,819 to Gentry et al.,the disclosures of which are hereby incorporated by reference.

Examples of concentric filter layouts that include granular carbon aredisclosed in European Patent Application No. 579,410 and U.S. Pat. No.3,894,545 to Crellin et al.

The plug-space-plug design typically comprises a pair of spaced-apartfilter plugs and a bed of granulated, activated carbon in the cavity orspace therebetween. In their manufacture, a procession of spaced-apartfilter plugs is established along a continuous ribbon of plug wrap. Theplug wrap is then partially folded about a portion of the plugprecession and granulated carbon material is poured or otherwiseintroduced into the spaces defined between the partially enwrappedfilter plugs. The plug wrap is then glued and closed, and the resultantcontinuous rod is then cut in well-defined locations according to adesired length, usually in the form of multiples of the filter elementactually utilized on the filter-tipped cigarette itself.

Cavity filling apparatus known in the art may be utilized in themanufacture of filter components such as shown in FIGS. 1 and 2. U.S.Pat. Nos. 4,214,508, 5,221,247, 5,322,459, 5,542,901 and 5,875,824illustrate and describe such cavity filling apparatus and thesedisclosures are incorporated herein by reference.

With machines and carbon materials of the prior art, process controlusually suffered at high machine speeds from inconsistent metering,scattering and pulverization of the granular material. Consistencyamongst filter rods would suffer, and some cavities would be less filledthan others.

For example, certain prior “charcoal” metering devices contain a supplyof granular carbon in a hopper and allowed the rim of a rotatingmetering wheel to rotate through the relatively stationary collection ofgranular carbon. Such an arrangement created a pulverizing action uponthe granular carbon, which action generally increased with machinespeed. Ricochet and escape of particulate matter during manufacturingoperations with prior machines and materials often created unacceptabledeficiencies in the final product (such as smears or incompletefillings) and precipitate undesirable machine “down-times” to effectclean-up of the machine and the surrounding work environment.

Granulated carbon, being a collection of irregularly shaped andvariously sized particles, tends to pack into a given volume of spaceinconsistently from one filling operation to the next. Accordingly,heretofore incomplete and inconsistent filling of cavities would plagueautomated filter rod making. The irregular packing would also createundesirable channels through the bed that would allow passage ofsubstantial portions of mainstream smoke through or around the bed suchthat interaction between the mainstream smoke and the granular carbonwould be lessened.

It has been known to include granulated, activated carbon materials incigarette filters to promote removal of constituents from mainstreamsmoke. As used heretofore in cigarette filters, these granular forms ofcarbon have been constructed by carbonizing an organic material such asnut shells or a wood material, and “activating” the carbonized materialby subjecting it to a heat treatment at approximately 800 to 1000degrees Celsius with steam or carbon dioxide. The activation treatmentof the material results in a porous (honeycomb-like) internal structureand a very large specific surface area, typically in the range of 300 to2500 square meters per gram as measured by the Brunauer, Emmett & Teller(“BET”) method for activated carbon.

However, such granulated, activated carbon materials have surfaceroughness and shapes which are irregular and inconsistent from granuleto granule. These irregularities and inconsistencies of granulatedcarbon materials create problems in the commercial production ofcarbon-bearing cigarette filter rods and cigarettes. For example, theirregular shapes exacerbate ricochet of the particles as they are fedthrough filter rod making machines, which event dirties the product witherrant carbon particles, puts dust into the work environment and createsa need for a shut-down to clean the rod making machine and leads toinconsistent and less complete filling of the cavities in theplug-space-plug filter rods.

Granulated, activated carbon materials also are known to have asignificant impact on the taste of a cigarette, in that their randomlybroad range of pore size distribution tends to capture not only gasphase components of a mainstream tobacco smoke, but also portions of theparticulate phase, i.e., some or a great number of tar constituents thatcontribute taste and flavor to the cigarette smoke. Granular activatedcarbons that are constructed from nut shells or wood are also known toinclude impurities, which are believed to be another possible cause ofoff-tastes attributed to the use of granulated carbon in cigarettes.

It is also understood that the process of activating granular carbontends to weaken the granule body, such that it is less robust and moreprone to fracture, pulverization and dusting when fed through meteringdevices of filter rod making machines. It is also understood that theactivation treatment adds cost to the manufacture of granulatedmaterial.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide acigarette having a cigarette filter incorporating a form of carboncapable of efficiently and effectively adsorbing gas phase componentspresent in mainstream cigarette tobacco smoke with a lesser impact onthe perceived taste of the cigarette when smoked.

Accordingly, another object of the present invention is to provide acigarette having a cigarette filter incorporating a form of carbonand/or other materials capable of efficiently and effectively adsorbinggas phase components of mainstream smoke, yet is physically robust towithstand automated filter rod making operations and does not requireexcessive activation treatment and associated costs thereof.

Yet another object of the present invention is to improve automatedproduction of carbon-bearing filter rods.

Yet another object of the present invention is to promote a morecomplete and consistent filling of cavities in plug-space-plug filtermanufacturing.

Still another object of the present invention is to obviate (lessen)material scatter and ricochet in the manufacture of filter plugs so asto lessen the occurrence of smeared product or dusting and the need toclean filter rod making machinery.

These and other objects are achieved with the present invention in whicha filter of a smoking article is constructed of activated carbon beadsof consistent spherical form and preferably of a pre-selected diameter,range of pore size distribution and activity level. With the presentinvention, there is achieved a carbon-bearing cigarette filter thatoffers uniformity of product formation, uniformity of productperformance, ease of achieving uniformity for both of these, andimproved absolute performance.

In a preferred embodiment, there is provided a plug-space-plug filterwhose cavity is filled with beaded carbon of a consistent sphericalshape and preferably of about the same size, preferably in the range of0.2 to 0.7 millimeter in diameter, more preferably in the range of 0.2to 0.4 millimeters at or about 0.35 mm diameter. At such sizes,sufficient and effective gas phase removal is achieved at moderate tolower activation levels, which preferably are in the range of 1600square meters per gram or less (as measured by the Brunauer, Emmett &Teller (“BET”) method). Accordingly, the robustness or hardness of thecarbon beads is preserved so as to enhance their resistance to fractureand formation of undesirable dust during automated manufacture of filterrods.

Maintaining bead size at or about a preselected diameter promotes asmoother flow and more consistent packing of the beads duringmanufacturing processes.

Activated beaded carbon is found to have a preponderance (greatestportion) of its pore size distribution in the micropore range (less than20 angstroms), which is believed to be optimal for the removal of gasphase constituents. It has also been found that activated beaded carbon(particularly pitch-based beaded carbon) has a smaller population ofmacropores (greater than 500 angstroms) compared to wood or coconutbased (granular) activated carbons.

Preferably, the beaded carbon is manufactured to have a pore sizedistribution predominantly in the range of micropores or small mesopores(50 angstrom diameter or less), with much fewer of the pores in therange of macropores (500 angstroms or greater), with the remainder ofthe pores lying within the range defined therebetween.

Beaded carbon may also be adapted to carry flavorants in a manner suchthat they are releasable to mainstream smoke.

BRIEF DESCRIPTION OF THE DRAWINGS

Novel features and advantages of the present invention in addition tothose mentioned above will become apparent to persons of ordinary skillin the art from a reading of the following detailed description inconjunction with the accompanying drawings wherein similar referencedcharacters refer to similar parts and in which:

FIG. 1 is a side elevational view of a cigarette comprising a tobaccorod and a multi-component filter, according to the present invention,with portions thereof broken away to illustrate internal details;

FIG. 2 is a side elevational view similar to FIG. 1, but showing acavity filled with spherical beaded carbon of two different sizes;

FIG. 3 is a cross sectional view of a single spherical bead optionallycomprising a core and a surface coating of flavorant;

FIG. 4 is an enlarged partial cross sectional view of a filter cavityfilled with spherical beaded carbon, showing point-to-point contactbetween the beads;

FIG. 5 is a side elevational view of another embodiment of the presentinvention comprising a tobacco rod and a multi-component filter withportions broken away to illustrate internal details;

FIG. 6 is a side elevational view of still another embodiment of thepresent invention comprising a tobacco rod and a multi-component filterwith portions thereof broken away to illustrate interior details;

FIG. 7 is a graph of puff-by-puff percent delivery of 1,3-butadiene forseveral different size beaded carbons;

FIG. 8 is a graph of puff-by-puff delivery of 1,3-butadiene as afunction of different PICA and beaded carbons, as well as delivery of1,3-butadiene from the control, a 1R4F standard cigarette; and

FIG. 9 is a bar graph showing the effect of carbon and non-adsorbentdiluents on the percent delivery of 1,3-butadiene.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a preferred embodiment of the present inventionprovides a cigarette 10 comprising a tobacco rod 12 and amulti-component filter 14 attached to the rod with tipping paper 16. Thefilter 14 is in the form of a plug-space-plug design with spaced apartcellulose acetate plugs 18, 20 and a cavity 22 therebetween filled witha beaded carbon 24 of a spherical form. Other filter configurations thatinclude a cavity filled with spherical beaded adsorbent material arealso within the scope of the present invention.

The spherical beaded carbon material 24 comprises individual beadspreferably of a pre-selected uniform diameter that have the advantageoustendency to contact each other at single points of contact whenestablished as a bed within a cavity of a plug-space-plug cigarettefilter. Such single-point contact produces a bed of the carbon materialwith minimal channeling or short-circuiting of tobacco smoke drawnthrough the cavity 22. Accordingly, maximum contact is achieved betweenthe gas phase of the cigarette smoke and the carbon surface of the beadsfor extremely efficient adsorption of the targeted gas phase components.

The filter cavity 22 is preferably filled with spherical carbon beads ofthe same size or in the alternative, comprise beads having two differentsizes, one larger than the other. Smaller size beads pack uniformlybetween larger beads, as shown in FIG. 2. Specifically, FIG. 2 is a sideelevational view similar to FIG. 1 with filter cavity 22 filled with acombination of large beads 26 and smaller beads 28 packed uniformlybetween the larger beads. The two sizes of beads may be selectedmathematically to maximize filing of the cavity 22 and thereby minimizebypass channeling at the outer edges of the cavity. In selecting themaximum bead diameter to be used, the diameter of the cylindrical filtercavity 22 is taken into consideration and optimal performance isachieved by utilizing beads having diameters in the range of 1/10 to1/40 that of the cavity diameter. When smaller beads 28 are alsoincluded in combination with the larger beads 26, the smaller beadsgenerally have a diameter of about 22% that of the larger beads. Apreferred mathematical relationship is a ratio of

$\sqrt{\left( \frac{3}{2} \right)} - 1$for the radius of the smaller beads 28 relative to the radius of thelarger beads 26.

As a further alternative, beaded material may also be selected toprovide flavorants to the smoke stream after other filter componentshave removed much of the gas phase components targeted for removal. Inone particular embodiment, the filter component may be similar to theone shown in FIG. 1 with an additional downstream cavity filled withflavored beaded material.

The tendency for single point contact between the spherical beadedcarbon 24 minimizes friction between the beads and allows them to flowrapidly during the manufacturing process in a manner similar to liquidsso as to self-assemble into a close packed array within filter cavity22. Such free flowability enables rapid and efficient filling of cavity22 with little or almost no wasted scatter of the carbon beads.

The carbon materials may be formulated into beaded configurations bytechniques known in the art. Moreover, when activated carbon is selectedas the spherical beaded carbon material, the carbons disclosed in U.S.Pat. Nos. 4,917,835, 5,456,868 and 6,033,506 may be utilized as well asother carbon formulations known in the art. The disclosures of thesepatents are incorporated herein by reference. Beaded carbon of aconsistent and true spherical form may be obtained from the KurehaChemical Industry Co., Ltd. of Japan or Mast Carbon Ltd, Henley Park,Guilford GU3 2AF, United Kingdom.

As noted above, spherical beaded carbon material 24 immediately packsinto a close-packed array with minimal formation of channels which mightotherwise reduce the efficiency of the filter bed within the filtercavity 22. This is a direct result of the point-to-point contact betweenthe smooth surfaced beads of material. Such uniform packing promotesless variation in the filters produced as well as less variation intheir overall performance. Unlike granular bed packings which oftensettle thereby producing formation of bypass channels or other voidspaces, filter cavity 22 is substantially completely filled withspherical beaded carbon material during the manufacturing process withno appreciable settling thereafter.

Referring to FIG. 5, another preferred embodiment of the presentinvention provides a cigarette 10A comprising a rod of smokable material12 such as shredded tobacco and a multi-component filter 14 attached tothe rod 12 with a tipping paper 16. Upon lighting of the cigarette 10A,mainstream smoke is generated by and drawn from the tobacco rod 12 andthrough the filter 14.

Herein, the “upstream” and “downstream” relative positions betweenfilter segments and other features are described in relation to thedirection of mainstream smoke as it is drawn from the tobacco rod 12 andthrough the multi-component filter 14.

Preferably, the filter 14 comprises a first, upstream carbon-bearingsegment 50 and a mouth end (mouthpiece) component 52. In thisembodiment, the carbon-bearing segment 50 comprises a plug-space-plugfilter sub-assembly that includes a central filter component 54, atobacco end component 56 in spaced apart relation to the central filtercomponent 54 so as to define a cavity 58 therebetween filled withspherical beaded carbon material 24, such as activated beaded carbon.The tobacco end component 56 is located adjacent to the tobacco rod 12and preferably, comprises a plug of cellulose acetate tow of lowresistance to draw (“RTD”).

As discussed above, the spherical beaded carbon material 24 comprisesindividual beads that contact each other at single points. Suchsingle-point contact produces a bed of the carbon material with minimalchanneling or short-circuiting of tobacco smoke drawn through the cavity58. Accordingly, maximum contact is achieved between the gas phase ofthe cigarette smoke and the carbon surface of the beads for extremelyefficient adsorption of the targeted gas phase components.

Moreover, as noted above, the carbon materials may be formulated intobeaded configurations by techniques known in the art. When activatedcarbon is selected as the spherical beaded carbon material, the carbonsdisclosed in U.S. Pat. Nos. 4,917,835, 5,456,868 and 6,033,506 may beutilized as well as other carbon formulations known in the art. Thedisclosures of these patents are incorporated herein by reference intheir entirety for all useful purposes.

The mouth end (buccal) component 52 is preferably in the form of acellulose acetate plug or other suitable fibrous or webbed material ofmoderate to low particulate removal efficiency. Preferably, theparticulate removal efficiency is low, with the denier and grand totaldenier being selected such that the desired total RTD of themulti-component filter 14 is achieved.

Preferably at least some, if not all of the carbon bed 24 isflavor-bearing or otherwise impregnated with a flavor.

Still referring to FIG. 5, the central filter component 54 of themulti-component filter 14 preferably comprises a plug 60 of fibrousfilter material, preferably cellulose acetate tow of a moderate to lowparticulate efficiency and RTD, together with one or more flavor-bearingyarns 62. As mainstream tobacco smoke is drawn through the centralfilter component 54 and along the yarn 62, flavoring is released intothe stream of mainstream smoke. Flavor-thread bearing filter plugs maybe obtained from the American Filtrona Company, 8410 Jefferson DavisHighway, Richmond, Va. 23237-1341 and a suitable construction for thecentral filter component 54 is described in U.S. Pat. No. 4,281,671,which patent is hereby incorporated by reference in its entirety for alluseful purposes.

Preferably one or more circumferential rows of perforations 64 areformed through the tipping paper 16 at a location along the centralcomponent 54 and downstream of the bed of flavored beaded carbon 20,preferably at the upstream end portion of the central component 54adjacent to the bed 24. The preferred placement maximizes distancebetween the buccal end 66 of the cigarette and the perforations 64,which preferably is at least 12 mm (millimeters) or more so that asmoker's lips do not occlude the perforations 64. Preferably, the levelof ventilation is in the range of 40 to 60% and more preferablyapproximately 45 to 55% in a 6 mg FTC tar delivery cigarette.

The beaded carbon bed may comprise at least 70 to 120 mg (milligrams) orgreater of carbon in a fully filled condition or 160 to 180 mg orgreater of beaded carbon in a 85% filled condition or better in thecavity 58.

By way of example, the length of tobacco rod 12 is preferably 49 mm, andthe length of the multi-component filter 14 is preferably 34 mm. Thelength of the four filter components of cigarette 10A is as follows: thetobacco end component 56 is preferably 6 mm; the length of the beadedcarbon bed 24 is preferably 12 mm for carbon loading of 180 mg; thecentral component 54 is preferably 8 mm; and mouth end component 52 ispreferably 8 mm.

Tobacco rod 12 may be wrapped with a conventional cigarette wrapper orbanded paper may be used for this purpose. Banded cigarette paper hasspaced-apart integrated cellulose bands 68 that encircle the finishedtobacco rod of cigarette 10 to modify the mass burn rate of thecigarette so as to reduce risk of igniting a substrate if the cigarette10A is left smoldering thereon. U.S. Pat. Nos. 5,263,999 and 5,997,691describe banded cigarette paper, which patents are incorporated hereinin their entirety for all useful purposes.

Referring now to FIG. 6 another preferred embodiment provides a modifiedcigarette 10B with the same filter segments as cigarette 10A of FIG. 6,but with a slightly different mutual arrangement of the segments, andsimilar reference characters are used to identify similar parts. Incigarette 10B the flavor-releasing yarn element 62 is located in themouth end component 52 at the buccal (mouth) end of the cigarette 10B,downstream from the flavored beaded carbon bed 24 and spaced therefromby the central component 54. In this embodiment, a plasticizer such astriacetin may be applied to the flavor yarn 62 to hold the yarn in placewithin component 52 and prevent the yarn from being draw out of thefilter during smoking. Alternatively, the flavor yarn 62 may be braidedtogether to achieve the same result. As in the embodiment of FIG. 5,ventilation 64 is provided at a location along the central filtercomponent 54 adjacent to but downstream of the flavored beaded carbonbed 24.

Activated beaded carbon material for use in the above describedcigarette filters may be manufactured by many known bead makingprocedures such as described in U.S. Pat. Nos. 3,909,449 and 4,045,368,and GB patent 1,383,085, for example, all of which are incorporatedherein by reference for all useful purposes. In many instances thestarting materials comprise pitch from petroleum and coal processing.Fundamentally, any meltable carbon-bearing substance (or carbonprecursor) is sufficient if it can be suspended in a fluid so as toestablish a spherical shape and solidified and thereafter carbonized andactivated.

There are great advantages in machine operation with beaded carbon overmore traditional particulate or granulated carbon (such granulatedcarbon as manufactured and sold by PICA USA Inc, 432 McCormickBoulevard, Columbus, Ohio 43213-1585). It has been discovered that, witha filter rod making machine set to provide a loading of 180 mg ofgranular carbon in a 12 mm cavity of a cigarette filter at an average86% fill level, the rod making machine without adjustment of machinesettings and at the same amount of carbon and the same length cavity,beaded carbon on average achieved an approximately 91% fill by volume atsatisfactory factory machine speeds, for example 1500 plugs per minute.Furthermore, it was discovered that operation of the beaded machine withbeaded carbon produced considerably less dust and that the extraneouscarbon collected by the machine was reusable and not fractured as isoften the case with granular carbon.

Another aspect of the present invention is the improved taste of acigarette that includes beaded carbon in the filter instead of granularcarbon. As explained more fully below, it has been found that based on 1to 7 point preference scale, American smokers rated a preference levelof a control cigarette with no carbon at a highest level (consistentwith their preference for carbon-free filters) and the same smokersrendered a preference level for a granular carbon cigarette at a lowerlevel, but when they smoked the same cigarette model with beaded carbon,their preference level rose to a level intermediate to the other tworatings. Such results evidence a significant enhancement in the likingscore with beaded carbon over the granular carbon model.

Activated beaded carbon is found to have a significant portion of itspore size distribution in the micropore and mesopore range (less than 50angstroms) with a relatively small distribution in the macropore rangeof greater than 500 angstroms. Not wishing to be bound by theory, it isbelieved that with the smaller count of macropores, beaded carbon hasless tendency to capture elements of tar from mainstream smoke andinstead lets flavor components of the smoke pass through the bed ofcarbon beads. In contrast, granular (PICA) carbon has a large portion ofpore size distribution in the macropore size range (a size range at orgreater than 500 angstroms), which tends to capture larger particlescomprising tar and flavor.

Additionally, granular carbon is constructed from organic materials suchas coconut shells, nut shells or wood, and its natural origin isbelieved to contribute a far higher ash count and presence of variousmetals and other materials and impurities, which are not found in beadedcarbon. This aspect is also believed to contribute to beaded carbonhaving a favorable subjective impact over granular carbon.

There are three central concerns with respect to machinability and theselection of a carbon material for cigarette filter applications. Oneconcern is the tendency of the rod making machine itself to produce dustduring cigarette manufacturing operations. Dust can continue to be aproblem in the handling of the products. Another concern is the cost ofexecuting the heat treatment for activating carbon. The greater the burnoff, the greater the weight of starting material that is wasted.Additionally, at higher activity levels, as a result of the carbonlosing mass and density, the carbon becomes more friable. Furthermore,there are limitations on how short a cavity can be established andfilled in plug-space-plug filter rod making operations. Presently, withfilter rod making machines, at least approximately 4 to 6 mm of cavitylength is preferred. Cavities of lengths less than 4 mm createmanufacturing difficulties and are not preferred.

Gas phase removal efficiency is impacted by particle size and beaddiameter, the smaller beads being the more efficient. Additionally, as ageneral matter, the more a given carbon is activated, the more efficientit is at gas phase removal, however, machinability (dusting factor) andcost of the activation treatment are countervailing considerations as tohow much activation is desirable. Balance is struck by reducing beaddiameter to a preferred range of bead diameter of approximately 0.2 mmto 0.7 mm, more preferably 0.2 to 0.4 mm, at an activation levelequivalent to a specific surface area in the range of 1000 to 1600square meters per gram BET (as measured by the Brunauer, Emmet & Tellermethod, hereinafter “m²/g BET”), more preferably in the range of 1100 to1300 m²/g BET. However, extremely small beads tend to pack so closely ina filter cavity that they impose an extra amount of pressure drop acrossthe cavity to an extent which may not be desired. In some applicationssuch as the preferred embodiments, excessive pressure drop is preferablyto be avoided. Accordingly, the more preferred spherical beaded size isapproximately 0.35 mm in diameter. The preferred ranges of size alsopromote proper and clean operation of the filter rod making machine.

The smaller the carbon bead, the more closely packed become the beads,which elevates pressure drop. Accordingly, the tendency toward an eversmall bead diameter to capture gas phase removal efficiency is counteredby the need to stay within the predetermined boundaries on pressure dropacross the filter so as to say within expectations of smokers withrespect to resistance to draw (RTD) upon smoking a cigarette.

FIG. 7 is a graphical representation of puff-by-puff delivery of1,3-butadiene from the mouth end of a cigarette for different carbonbead-size diameters. The given beaded carbon materials comprise 75 mg of0.7 mm-diameter activated beaded carbon in a 2.7 mm bed length (curve100 in FIG. 7), 75 mg of 0.5 mm diameter activated beaded carbon in a2.6 mm bed length (curve 102), and 75 mg of 0.35 mm diameter activatedbeaded carbon in a 2.5 mm bed length (curve 104). Each cavity was in acompletely-filled condition.

Still referring to FIG. 7, it has been found that smaller bead diameterincreases performance in the removal of 1,3-butadine, and is fullyeffective throughout all puffs. In particular, it has been found that 75mg of beads supplied by the Kureha Chemical Industry Co., Ltd. of Japanat 0.35 mm diameter with a fully filled 2.5 mm cavity length willcapture essentially all of the 1,3-butadiene of the cigarette throughoutall eight of its puffs, even at relatively low surface area-to-massvalues.

The surface area activity level of the beaded material in FIG. 7 is inthe range of 1000 to 1600 m²/g BET, preferably, 1100 to 1300 m²/g BET.It should be noted that the result represented by line 104 is an almostcomplete removal of 1,3 butadiene and that line 102 represents asignificant (near 90%) reduction in 1,3 butadiene.

FIG. 8 is a graphical representation of puff-by-puff delivery from themouth end of a cigarette of 1,3-butadiene for different diameters ofbeaded carbon: 75 mg of 0.35 mm diameter carbon beads in a 2.5 mm lengthcavity (curve 108 in FIG. 8), 48 mg of 40×60 mesh granular (PICA) carbonin a 2.5 mm length cavity (curve 110), 46 mg of 20×50 mesh granular(PICA) carbon in a 2.5 mm length cavity (curve 112), 180 mg of 20×50mesh granular (PICA) carbon in a 12 mm length cavity (curve 114), and a1R4F cigarette standard control (curve 116).

Comparing FIGS. 7 and 8 one finds that 40×60 mesh granular carbon with a48 mg loading in a 2.5 mm cavity (curve 110 in FIG. 8) presentsessentially the same result as from a 0.35 mm diameter beaded carbon(curve 108 in FIG. 7). However, the 40×60 mesh PICA carbon is known tobe extremely difficult to handle in filter rod making machine operations(significant and confounding dusting). However, 0.35 mm diameter beadedcarbon, at a 75 mg loading is readily handled without significantdusting in machine operations both because of the favorable general flowcharacteristics of beaded carbon and its greater density and hardness,(being at a lower to moderate level of activation). Accordingly, thebeaded carbon achieves the same performance as super fine granular(PICA) carbon, yet at a size readily handled by cigarette manufacturingmachinery. Such is a significant advantage.

Generally, the carbon beads are denser and harder material than PICAparticulate carbon. Accordingly, there is less dusting in manufacturingand handling of cigarette filters with beaded carbon and it tends tofill cavities in more orderly fashion and more completely than granularcarbon does.

With 0.35 mm diameter beaded carbon at a 75 mg loading level at a filledcavity condition, excellent gas phase removal efficiency is achieved,such as that represented by line 104 in FIG. 7. However, such carbonloading fully fills a 2.5 mm long cavity at a standard cigarettecircumference (24 millimeter), which cavity length is difficult tomanufacture. Accordingly, it may be preferred to include with theactivated beaded carbon other beads of similar or preferably the samesize, but with little or no activity to save costs and to enhancemachinability. Experiments combining 75 mg of beaded carbon with glassbeads at a volumetric split of ⅓ beaded carbon and ⅔ beaded glass showedessentially the same performance in gas phase removal as with the same75 mg loading acting by itself. Accordingly, it may be preferred to mixa 75 mg loading of activated beaded carbon with additional beads ofunactivated carbon, preferably of the same size in diameter ofsufficient mass to fill a 6 mm long cavity or such additional amountthat may be required to fill the cavity traditionally employed by thecigarette manufacturer. Such combination of activated and non-activatedcarbon beads produces the same results at a lesser cost since it is notnecessary to entirely fill the cavity with the more expensive activatedcarbon beads. A further advantage of this discovery is that a cigarettemanufacturer can preselect a cavity size for his spectrum of cigarettebrands and have a freedom to select different amounts of carbon fordifferent bands or packings and fill any remainder of space in thepreselected cavity with inactivated (or less activated) beaded material,beaded material flavor carriers, or other suitable filler material. Assmoker preferences change or in response to other circumstances, theproportion of activated beaded carbon in the filter may be changedwithout complications such as having to change the cavity size in thecigarette layout or size changing the filter and cigarette productionmachinery. Such is a significant advantage in cigarette operations

FIG. 9 is a bar chart that illustrates relatively similar results on thetotal percent delivery of 1,3-butadine for filters with beaded carbonalone and beaded carbon dispersed with a non-adsorbent diluent. Bar 120in FIG. 9 is for a 1R4F cigarette standard control and shows about 86%delivery of 1,3-butadiene from the mouth end of the cigarette afterabout eight puffs during the smoking process. Bar 122 and 124 representa cigarette construction similar to FIG. 5, but with cellulose acetateand no carbon (bar 122) and 380 mg of glass beads and no carbon (bar124). After about eight puffs the total percent delivery of1,3-butadiene from the mouth end of each cigarette is high,approximately 91% for bar 122 and 82% for bar 124. Bars 126, 128 and 130each represent cigarette constructions similar to FIG. 5, but in eachinstance the filter cavity is filled with different materials. Thecigarette represented by bar 126 includes a cavity filled with 75 mg of0.35 mm diameter activated carbon beads. Approximately only 1% ofdelivery of 1,3-butadiene passes through the mouth end of the cigaretteof bar 122 after eight puffs, and similar results are achieved with thecigarettes represented by bars 128 and 130 where the filter cavities arefilled with 75 mg of 0.35 mm diameter activated carbon beads, but incombination with non-adsorbent diluents. The cigarette of bar 128includes 190 mg of glass beads dispersed with the carbon beads and thecigarette of bar 130 includes 380 mg of glass beads dispersed with thecarbon beads. In each instance the total percent delivery of1,3-butadiene from the mouth end of the cigarette after eight puffs isabout 2%. In summary, filters that include activated carbon beads incombination with non-adsorbent diluents produce approximately the sameresults as filters with an equivalent weight of activated carbon beadsin undiluted form.

The following Table 1 shows pore size distribution of activated carbonsincluding PICA carbon 20×50 mesh per inch and 40×60 mesh per inch aswell as beaded carbons having diameters of 0.7 mm, 0.5 mm and 0.35 mmfrom two different batches.

TABLE 1 Bulk * DFT Pore Volumes Density BET S.A. Micro Vol. Total Vol.Sample (g/cc) (m²/g) (cm³/g) (cm³/g) PICA 20 × 50 mesh 0.37 1587 0.54590.5983 PICA 40 × 60 mesh 0.39 1468 0.5566 0.5967 Beads Batch 1 0.57 11290.4614 0.4849 0.7 mm diameter Beads Batch 1 0.58 1247 0.4791 0.4906 0.5mm diameter Beads Batch 1 0.59 1289 0.4821 0.5154 0.35 mm diameter BeadsBatch 2 0.58 1150 0.4562 0.4618 0.5 mm diameter Beads Batch 2 0.58 12440.4750 0.5030 0.35 mm diameter * DFT: as calculated by DensityFunctional Theory which is a molecular-based statistical thermodynamictheory that allows relating the adsorption isotherm to the microscopicproperties of the system. (Reference: P. A. Webb and C. Orr, AnalyticalMethods in Fine Particle Technology, Micrometrics InstrumentCorporation, Norcross, GA, 1977, page 81.)

PICA carbon has a bulk density of approximately 0.37 grams per cubiccentimeters whereas activated beaded carbon of the preferred carbon hasa bulk density greater than 0.5, more preferably in the range of 0.55 to0.6 g/cm³.

It is to be realized that the beaded, activated carbons of the preferredembodiments may be mixed, combined or otherwise cooperating with otheradsorbants such as zeolites, molecular sieves, composite or layeredmaterials, clays, alumina, other metal oxides, metal silicates, andmetal phosphates, silica gels, and modified silica gels, such as3-aminopropylsilyl (APS) silica gel beads.

The following Table 2 shows the percent total delivery of the indicatedgas phase components versus a control 1R4F standard cigarette forcigarette filter constructions where a filter cavity such as shown inFIG. 5 is filled with the indicated materials.

TABLE 2 75 mg of 75 mg of 0.35 mm 0.35 mm diameter diameter 30 mg of 40mg of 75 mg of carbon carbon 0.35 mm 0.35 mm 0.35 mm beads and beads anddiameter diameter diameter 190 mg 380 mg carbon carbon 1R4F: carbonglass beads glass beads 380 mg beads and beads and Control beads(blended) (blended) glass beads 70 mg silica 60 mg silica Carbon Dioxide101 96 99 103 98 90 96 Propene 95 18 23 23 80 33 28 Hydrogen Cyanide 867 11 12 57 24 18 Ethane 90 76 78 79 77 72 70 Propadiene 100 18 34 32 12247 45 1,3-butadiene 86 1 2 2 82 7 4 Isoprene 94 3 2 2 97 4 4cyclopentadiene 94 3 3 2 59 6 4 1,3-cyclohexadiene 99 3 1 1 104 4 3me-cyclopentadiene 87 2 1 1 116 3 2 formaldehyde 87 21 18 20 137 15 12acetaldehyde 95 4 4 5 81 4 3 Acrolein 102 1 1 2 70 4 2 Acetone 99 1 0 086 0 0 Diacetyl 84 1 1 0 79 1 0 methyl ethyl ketone 101 1 0 0 98 0 0isovaleraldehyde 84 3 3 2 75 2 2 Benzene 96 2 1 1 96 5 3 Toluene 86 2 10 85 2 1 isobutryonitrile 78 0 0 0 62 0 0 methyl furan 90 2 2 1 122 6 32,5-dimethyl furan 88 3 1 1 180 4 2 hydrogen sulfide 91 13 19 18 51 2321 carbonyl sulfide 89 45 51 51 89 55 53 methyl mercaptan 93 29 28 31108 33 33 1-methyl pyrrole 90 0 0 0 69 0 0 Ketene 77 2 1 0 89 5 3acetylene 99 113 113 121 114 94 95 40 mg of 0.35 mm 50 mg of diameter0.35 mm 75 mg of 75 mg of carbon diameter 0.7 mm 0.5 mm beads and carbon46 mg 48 mg diameter diameter 60 mg silica beads and 20 × 50 40 × 60carbon carbon (blended) 50 mg silica PICA PICA beads beads CarbonDioxide 101 117 100 103 108 98 Propene 37 26 46 25 59 36 HydrogenCyanide 10 9 11 2 37 17 Ethane 71 88 75 75 89 76 Propadiene 59 43 80 5176 43 1,3-butadiene 5 0 8 0 43 11 Isoprene 3 1 4 0 34 7 cyclopentadiene3 2 5 0 39 9 1,3-cyclohexadiene 1 1 2 0 39 6 me-cyclopentadiene 1 1 2 050 5 formaldehyde 20 22 11 4 32 20 acetaldehyde 3 2 19 4 37 10 Acrolein2 1 3 0 36 8 Acetone 0 0 1 0 22 2 Diacetyl 0 0 1 0 15 3 methyl ethylketone 0 0 1 0 27 3 isovaleraldehyde 2 1 5 3 27 6 Benzene 1 1 2 0 29 5Toluene 1 0 2 0 23 4 isobutryonitrile 0 0 1 0 11 2 methyl furan 2 1 3 041 9 2,5-dimethyl furan 1 1 3 0 58 8 hydrogen sulfide 20 15 12 1 38 22carbonyl sulfide 64 58 79 70 82 57 methyl mercaptan 40 37 42 29 77 401-methyl pyrrole 0 0 0 0 17 1 Ketene 5 2 0 0 19 5 acetylene 108 119 92102 121 108

Preferably, flavor is added to the carbon beads by spraying flavorantupon a batch of activated carbon in a mixing (tumbling) drum oralternatively in a fluidized bed with nitrogen as the fluidizing agent,wherein flavorant may then be sprayed onto the carbon in the bed. Also,it is within contemplation of the present invention to locate flavorantson other filter components or the bed of carbon beads, standing alone,or any of the above with addition of flavorants being carried along oneor more plug wraps and/or the tipping paper.

One skilled in the art will appreciate the present invention can bepracticed by other than the described embodiments, which are presentedfor purposes of illustration and not of limitation. For example,cigarette filters may include beaded carbon entrained within a fibrousmass such as cellulose acetate tow. Also, optionally the spherical beadsmay each comprise a core and a surface coating of flavorant. The presentinvention is limited only by the claims that follow.

1. A cigarette filter comprising at least a pair of spaced apart solidfilter segments, a cavity between the segments with beaded, activatedcarbon therein, essentially all of the beads having a spherical form anda pre-selected diameter for removing at least one gas phase constituentfrom mainstream tobacco smoke, wherein the beaded, activated carbonfills at least 85% of the cavity, and a flavor releasing segmentdownstream from the beaded activated carbon.
 2. A cigarette filter as inclaim 1, wherein at least a portion of the beaded, activated carbon isflavored.
 3. The cigarette filter as in claim 1, wherein the beadedcarbon of spherical form has a diameter within the range ofapproximately 0.20 millimeter to 0.70 millimeter.
 4. The cigarettefilter as in claim 3, wherein the beaded carbon of spherical form has adiameter in the range of 0.20 millimeter to 0.40 millimeter.
 5. Thecigarette filter as in claim 4, wherein the beaded carbon of sphericalform has a diameter of approximately 0.35 millimeter.
 6. The cigarettefilter as in claim 3, wherein at least a portion of the beaded carbonmaterial has a specific surface area not greater than 1600 meterssquared per gram BET.
 7. The cigarette filter as in claim 6, wherein atleast a portion of the beaded carbon material has a specific surfacearea in the range of 1100 to 1300 meters squared per gram BET.
 8. Thecigarette filter as in claim 3, wherein the activated beaded carbon hasa density greater than 0.5 g/cm³.
 9. The cigarette filter as in claim 1,wherein the activated beaded carbon is of a predetermined amountsufficient to reduce 1,3-butadiene by approximately 90% or more.
 10. Thecigarette filter as in claim 9, wherein the predetermined amount isapproximately 70 to 180 milligrams of activated beaded carbon.
 11. Thecigarette filter as in claim 1, including a second beaded material oflesser or no activation when compared to the activated beaded carbon.12. The cigarette filter as in claim 11, wherein the second beadedmaterial comprises a beaded carbon of substantially the same diameter asthe activated beaded carbon.
 13. The cigarette filter as in claim 1,wherein the spherical beaded carbon comprises a first group ofindividual beads of substantially the same diameter and a second groupof individual beads of substantially the same diameter but smaller thanthe diameter of the beads of the first group.
 14. The cigarette filteras in claim 13, wherein the spherical beads of the second group have aradius which is approximately $\sqrt{\left( \frac{3}{2} \right)} - 1$that of the radius of the beads of the first group.